Circuit breakers are commonly found in substations and are operable to selectively open and close electrical connections. Modern medium to high voltage circuit breakers include automatic, electronically controlled actuating systems that recognize fault conditions and initiate trip sequences. These electronically controlled breakers may also be remotely actuated from an off-site location, such as a power utility operational control room.
Despite the highly automated nature of modern circuit breakers, the need still exists for reliable and safe means to manually actuate (open) the breaker. Manual tripping (opening) of a circuit breaker must follow through the stroke of the actuation with enough force to achieve proper contact velocities (i.e. the velocity the two contacts are drawn apart) regardless of the amount of energy remaining in the “wipe” contact springs. As the contacts erode, the amount of force and stored energy in the circuit breaker decreases and the force and energy required by the manual tripping device to open the circuit breaker increases. The design of the manual tripping device is such that it functions properly with the minimum amount of contact wipe spring compression on all phases (or worst case condition). Forces that must be overcome by a manual actuation mechanism include: the magnetic holding force of the magnetic actuators (from installed permanent magnets), weld break of any contacts if needed, operating friction and acceleration of mass in various parts. In medium voltage outdoor circuit breakers (i.e. 5 kV through 38 kV), the magnetic holding force of the actuator is based on the interrupting rating and requires enough holding force to withstand the forces generated by approximately 12 to 50 kA rms, asym fault current and possibly higher. This force is counteracted by the total “wipe” spring contact force acting on the actuator. The wiping spring contact force reduces the manual tripping force requirement, but the holding force of the actuator remains a significant value, and the resulting net latching force (manual tripping force required) can be over 1000 lbs in a circuit breaker with a high short circuit rating. In addition, the human operator should not be required to apply greater than a 50 lb force to a lever or handle to manually trip the unit.
Some prior art manual actuation devices incorporate an automatic spring charged mechanism for opening and closing operations. According to these designs, energy is transferred from a power device, such as an electric motor, and stored in a spring system which holds the charge indefinitely, even in the absence of control power to the motor. When triggered manually, the mechanism provides the tripping (opening) energy and operation of the circuit breaker. Such solutions are relatively more expensive, as they require an internal source of input power (electric motor). Further, if the spring charge is exhausted, no further operation is possible unless power is available to the input power source. Further, such mechanisms typically require a regular maintenance cycle, due to the use of the older electric motor and an excessive amount of small parts in the mechanism. Such maintenance cycles are disadvantageous, as operators prefer maintenance free equipment wherever possible.
Thus, there is a need in the art for a manual tripping mechanism that can initiate and complete the manual tripping operation without any motorized spring charging mechanism and is operable with reduced input force applied by an operator on the lever.